So as to have a variety of plant products such as fruit, vegetables and fresh flowers available in every country and during all seasons, regardless whether or not these products are raised in that particular country during the respective season, or even at all, there is a strong desire to create appropriate transport- and storage conditions for these products so that they can be stored for a prolonged period of time immediately following the harvest, and can still be sold to the consumer as fresh products without any loss of quality. Under appropriate conditions, the rather expensive transport of individual container units via airfreight can be replaced by the significantly more cost-efficient mass transport per sea freight. Furthermore, the longer storage times eliminate the fluctuating supply as a result of harvesting cycles.
The principal problem in the storage of plant products over a prolonged period of time is that they are living organisms with a metabolism and an energy requirement, whereby said metabolism must be maintained during storage.
By means of targeted manipulation, such as lowering the temperature, controlling the air humidity, a significant increase of the CO2-concentration and lowering the O2-concentration in the atmosphere of the storage facility, for example, the activity of the enzymes taking part in the breathing metabolism is lowered and thus the metabolism of the fruit is delayed during storage. Another advantage of this type of controlled atmosphere is that feeding pests in the storage spaces are exterminated. With fruit, one differentiates between climacteric fruits such as bananas, kiwis, tomatoes or apples, and non-climacteric fruits such as citrus fruits, for example. They are different in that they react differently to the composition of the atmosphere, and the plant hormone ethylene plays a different role during their ripening process.
The metabolism of plant products and fruits cannot be lowered any by lowering the O2-concentration. When the concentrations are too low, the energy that the plant product requires for metabolism is generated by a conversion to alcoholic fermentation, which causes the generated alcohol to accumulate in the stored product, leading to a drastic loss of quality.
An increased CO2-concentration during storage can influence the normal metabolism of the fruit with respect to storage positively in view of the glycolysis, the fermentation, the cancer cycle or the electron transport. However, their breathing hardly decreases in the pre-climacteric, whereas a significant reduction can be detected for climacteric fruit in the climacteric. On the other hand, for example, the peel of apples may scald [turn brown] if the CO2-concentration is too high and the storage temperatures are low, which renders the apples unfit for sale. Although adding antioxidants can reduce the degree of scalding, this type of treatment is not permitted in Germany. Furthermore, an excessive CO2-concentration can also lead to an increased C2H4-production, irregular ripening, suppressed or more difficult physiological processes and an increased susceptibility for rotting.
Ethylene is a plant hormone that plays a key role in a great number of various growth phases and -processes of plants and fruit, such as germination, sprout growth, flowering, wilting, ripening of the fruit, senescence, etc. However, it is also produced by the plants in stress situations such as a lack of water, over-flooding, heat, coldness, fungus- and bacteria attacks and mechanical injury.
The so-called Yang cycle describes the biosynthesis of the ethylene:                L-methionine→S-adenosyl-L-methionine (AdoMet)→        1-aminocyclopran-1-carboxylic acid (ACC)→ethylene        
The enzymes that are relevant for the control of the ethylene production are the ACC synthase, i.e., the conversion from AdoMet to ACC, and the ACC oxidase, the oxidation from ACC to ethylene.
Thus, one takes advantage of the influence of ethylene on the ripening process of climacteric fruits. In this way, the ripening process can be irreversibly induced by exogenous ethylene in the atmosphere surrounding the fruit. For example, the ethylene content in the atmosphere of the storage space is increased by a multiple shortly before the sale of stored, unripe bananas to bring the bananas to a full ripeness.
Lower temperatures—so-called cold stress—stimulates the autocatalytic ethylene production in climacteric fruits. The ethylene induced by cold stress is generated in the course of normal biosynthesis (Yang cycle), whereby the conversion capacity from ACC to C2H4 increases as the temperature drops.
EP 0 703 727 B1 discloses a method for the transport of quickly perishable goods, especially freshly harvested, unripe bananas, where the bananas are first stored in a shipping- and ripening container and brought to a temperature of 14 to 15° C. in said container. To initiate the ripening process of the bananas, the bananas are gassed with ethylene for up to 48 hours. Then the atmosphere containing ethylene is displaced by a controlled atmosphere with a reduced oxygen content of 2% to 10%, whereby a minimum ethylene content that is sufficient to support a continuous ripening process is supposed to be retained. Finally, normal atmospheric conditions are restored in the container and the bananas are unloaded.
In addition, WO 86/01296 discloses a detector for the verification of ethylene in the storage of the transport of plant products. Said detector is supposed to determine when an ethylene limit value has been reached in the storage facility, so that the storage facility can be aerated by turning on a ventilator, and the ethylene concentration can be lowered in this way. Specifically, this is supposed to reduce the energy costs created by the continuous aeration of the storage space for a permanent discharge of the ethylene emitted by the products. The detector is also supposed to be used to check the concentration of ethylene in the atmosphere of the storage room when ethylene is added to the atmosphere to speed up the ripening process.
With all known methods, however, it cannot be avoided that some of the plant products perish. For one, this is attributed to the fact that the quality at the time of storage and during the course of the storage or the transport is not known.